RFR: 8300109: RISC-V: Improve code generation for MinI/MaxI nodes

[Fei Yang]

As described by the issue, code generation for MinI/MaxI nodes on RISC-V could be improved when one of the source register is the same as the destination register. Also the code could be further simplified when that source register is constant 0 making use of the dedicated zero register of the architecture. This adds extra match rules for those cases. 

Testing:
- [x] Tier1-3 tested with release build on HiFive Unmatched board.
- [x] Run non-trivial benchmark workloads (dacapo, specjvm, renaissance, etc) with fastdebug build on HiFive Unmatched board.

-------------

Commit messages:
 - 8300109: RISC-V: Improve code generation for MinI/MaxI nodes

Changes: https://git.openjdk.org/jdk/pull/11988/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11988&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300109
  Stats: 90 lines in 1 file changed: 88 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/11988.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11988/head:pull/11988

PR: https://git.openjdk.org/jdk/pull/11988